Researchers in the United States have conducted a study demonstrating the real-world effectiveness of the Pfizer-BioNTech and Moderna coronavirus disease 2019 (COVID-19) vaccines at preventing infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
Importantly, Mark Thompson from the CDC COVID-19 Response Team and colleagues also showed that the vaccines were highly effective at reducing viral load, febrile symptoms, and the duration of illness among individuals who developed breakthrough infections despite having been vaccinated.
The large prospective study of almost 4,000 people found that full vaccination (with two doses) was 91% effective at preventing SARS-CoV-2 infection, while partial vaccination (with one dose) was 81% effective.
Among those who became infected, partially or fully vaccinated individuals had a lower level of viral RNA, a lower risk of developing febrile symptoms and a reduced duration of illness compared with unvaccinated individuals.
The researchers say that if further data confirm that these vaccines reduce the viral load and, in turn, blunt the infectivity of SARS-CoV-2, this would suggest that the vaccines are not only highly effective at preventing infection, but could also reduce the impact of breakthrough infections.
This has significant implications for essential and frontline workers, given their potential to spread the virus through frequent close contact with patients, co-workers, and the public, says Thompson and colleagues